1. Field of the Invention
This invention relates generally to the field of free-space optical communications. More specifically, the invention relates to the use of adaptive optics (including for example tip/tilt correction) as an enhancement to a free-space optical communications link.
2. Description of the Related Art
With recent advances in technology, there is an increasing interest in the use of free-space optical communications for various applications. For example, much of the current telecommunications infrastructure is based on the transmission of optical signals via optical fibers. While the use of fiber optics has increased the capacity and efficiency of data transmission, there are many situations where the installation of new fiber is not the best solution. As a result, there is interest in augmenting the telecommunications infrastructure by transmitting optical signals through the free-space of the atmosphere.
Free-space optical communications links can also be used advantageously in applications outside of the telecommunications infrastructure. Compared to other communications technologies, a free-space optical communications link can have advantages of higher mobility and compact size, better directionality (e.g., harder to intercept), faster set up and tear down, and/or suitability for situations where one or both transceivers are moving. Thus, free-space optical communications links can be used in many different scenarios, including in airborne, sea-based, space and/or terrestrial situations.
However, in many of these potential applications, the free-space optical communications link suffers from optical aberrations. For example, changes in atmospheric conditions can be a significant impediment to the accuracy, reliability and efficiency of free-space optical communications systems. Wind, heat waves, man-made pollutants and other effects can create constantly changing aberrations. This, in turn, can degrade the quality of the optical signal that is available at the receiver, resulting in degradation of the overall quality and efficiency of the communications channel.
Adaptive optics can compensate for these aberrations, thus improving the performance of a free-space optical communications link. However, current free-space optical communications links that have adaptive optics capability typically use separate detectors for data detection and for wavefront sensing. The incoming optical beam typically is divided by a beamsplitter, with one portion directed to the data detector and the other portion to the wavefront sensor. However, this requires that the data detector and wavefront sensor be accurately registered with respect to each other. The use of two separate detectors and the resulting registration requirement adds cost and complexity to the overall system and can also reduce the reliability of the system.
As a result, it would be advantageous for adaptive optics systems to eliminate the need for two separate detectors.